2n - 3 = 9
If you are solving for n:
Isolate it by doing the opposite of PEMDAS; Also, what you do to one side you do to the other (because of the equal sign)
2n - 3 = 9
2n - 3 (+3) = 9 (+3)
2n = 12
2n/2 = 12/2
n = 6
n = 6 is your answer
hope this helps